The blue-blooded investor, whose relationship with Mr Deripaska featured during a holiday incident in Corfu last summer, is thought to be one of four main investors to sign up for shares ahead of Rusal’s listing which is predicted to be one of the biggest of 2010.

The others are Paulson & Co, the American hedge fund giant run by John Paulson; Robert Kuok, the Malaysian-Chinese tycoon; and Vnesheconombank, or VEB, the Russian state development bank. The investors will be guaranteed shares in the flotation in exchange for a pledge not to sell them for a number of months.

Rusal plans to raise $2bn (£1.25bn) from selling a 10pc stake with the company set for a primary listing in Hong Kong and a secondary listing in Paris on January 29.

Rusal had hoped for a valuation of $30bn from the listing but reports suggested that this could be reduced to $17bn-$22bn next month.

Mr Rothschild is thought to be buying a stake through NR Investments, a private vehicle. He has close ties with Mr Deripaska and has acted as his investment adviser.

Their relationship came to light in media reports about a holiday meeting involving shadow chancellor George Osborne and Mr Deripaska aboard the Russian oligarch’s yacht, Queen K, in Corfu in 2008.

Rusal has planned the initial public offering in an attempt to reduce its $17bn debt burden. The company’s debts doubled last year after it went on an acquisition spree shortly before commodity prices collapsed.

Aluminium tumbled 36pc in 2008 on the London Metal Exchange.

Regulators in Hong Kong approved Rusal’s listing application earlier this month but said the offer would not be open to retail investors because

the company’s debt levels made it high risk. Rusal is set to become the first Russian firm to list in Hong Kong.

The pre-marketing is planned to start on Monday. The investor roadshow is set for January 12, starting in Hong Kong and moving through Singapore, the UK, Europe and the US.

Bank of China International, BNP Paribas, Bank of America Merrill Lynch and Credit Suisse are bookrunners on the deal.